GHCN Adjusted Data Isn't Good Enough for D'Arrigo et al

D’Arrigo, Wilson et al 2007 is an interesting article on the Divergence Problem, about which I plan to post from time to time. Since we’ve been discussing temperature data recently – with special discussions of GHCN data problems in Russia, China and Australia, I thought that it would be interesting to draw attention to an interesting aside in D’Arrigo, Wilson et al 2007 in which they reject GHCN adjusted data for Dawson, Yukon on the basis that it has inserted an unrealistically large trend.

The discussion comes up in their discussion of the D’Arrigo et al 2004 discussion of Twisted Tree Heartrot Hill, a site discussed previously at CA here and discussed in McIntyre and McKitrick 2003 (Mann used a version of this data which was obsolete even in 1997). D’Arrigo et al observe a “Divergence Problem” in which temperatures rise and ring widths decline in the late 20th century – for which they (plausibly in my opinion) postulate an upside-down U relationship:

The trees at this location, when compared with local climate data for Dawson, Yukon Territory, appeared to have reached a temperature threshold due to recent warming. The positive ring-width/temperature relationship weakened such that a pre-1965 linear model systematically overpredicted tree rings at this site from 1965—1999. A nonlinear model showed an inverted U shaped relationship between this chronology and summer temperatures.

In trying to mitigate the results of the D’Arrigo 2004 analysis, D’Arrigo, Wilson et al 2007 observe that there is a much lesser temperature trend in the Canadian data than in the GHCN adjusted data. They say (their figure below)

D’Arrigo et al. (2004a) utilized a version of the Dawson instrumental temperature record that had been adjusted for inhomogeneities (Global Historical Climate Network (GHCN), V. 2; Peterson and Vose, 1997)… However, the corrected Dawson station data from the Historical Canadian Climate Database (HCCN, Vincent and Gullett, 1999) have less pronounced positive trends than the GHCN version used in D’Arrigo et al. (2004a).

Caption: Fig. 2. Time series plots of mean July—August temperatures for the Dawson meteorological station, Yukon Territory. The data were taken from the homogeneity corrected Global Historical Climate Network (GHCN, Peterson and Vose, 1997) and Historical Canadian Climate Network (HCCN, Vincent and Gullett, 1999) data-sets. The lines denote the linear trend of each record over the 1900—2000 period.

The difference between the GHCN and Canadian trends are 4.42 deg C and 1.38 deg C! For comparison, here are plots of July-August temperatures for Dawson (71966000) as collated from GHCN Unadjusted and Adjusted Versions. The shape of the GHCN Adjusted version matches the plot in D’Arrigo et al 2007, but the version that I downloaded comes forward a little more to the present. The unadjusted version is different again from the Canadian version.

Figure 2. Dawson 719660000 versions for July-August average from GHCN.

Jerry Brennan observed that GISS does its own adjustments. So here are the adjusted and unadjusted versions at GISS, which are virtually identical and similar to the GHCN unadjusted version. (The two overlay almost exactly so I’ve re-plotted one as dots as well.)

In 2007, D’Arrigo, Wilson et al didn’t think that the GHCN adjusted data was appropriate. We know that Rob Wilson’s a thoughtful guy and D’Arrigo’s a leading authority – who are we to argue with this decision.

One more oddity: all these various versions of the Dawson data end in 1989. You can find Dawson temperature up to the minute online here yet the GHCN and GISS versions don’t appear to have been updated in nearly 20 years.

24 Comments

The upside-down U hypothesis is a good starting point, but until a plant physiologist measures the effect of temperature (eg, reduced carbon uptake) on the sampled trees it remains speculation. Shifts in precipitation patterns can just as easily inhibit springwood if summer drought conditions begin a few weeks earlier than they used to.

If Rob is right, the proxy data enables us to identify a defect in the GHCN adjustments. I presume that Dawson is not the only location where GHCN has used this adjustment process and that there would be a varieety of flawed adjustments. I wonder what data sets use adjusted GHCN data and would be impacted by Rob’s observation.

Can someone explain to me why all of these “corrections” are being made? It would seem to me that someone, somewhere, is trying to tinker with history to make a position stronger. But that would be paranoid, right?

Regardless of which versions prove eventually to be correct (if any) does not this multiple versions of temperature series provide, once again, another piece of data for cherry picking. You picks your months, your lags, your TRs and/or a combination of TRs and MXDs, your trees, your best regressions and now your temperature series. Dendros must have excellent reasons for these selection processes, otherwise they would be as suspect as some stock investment schemes I have seen.

I’m having trouble understanding the implications of differences between GHCN and HCCN using mean July’€”August temperatures. Can I get someone to connect the dots? I guess I’m still new to the divergence issue.

To clarify – We make no definitive statement about which instrumental version is better. We basically state that the use of the HCCN data would change the results of D’Arrigo et al. (2004) with regards to the thresholds. The loss in sensitivity in the recent period is still there though.

The apparent disparity between these time series suggests a somewhat more cautious interpretation than that stated by D’Arrigo et al. (2004a). If the HCCN version is closer to reality, then the divergence at the TTHH site would still be present but considerably weakened, and the estimates of threshold optima would need to be modified accordingly. However, the overall conclusion would still be the same: i.e. that there is a divergence between tree growth and temperature at this site in the recent period (D’Arrigo et al. 2004a).

However, this does highlight an important issue. Tree-ring based reconstructions are “at the mercy” of the instrumental data and if there are problems with the predictand data, then it will affect our calibrations.

#8
I agree. One odd thing, among a vast array of oddities, is that many of the Arctic stations do not show this pattern – e.g., Greenland station records,. Some of those that do are also candidates for a UHI effect because of population and SOL shifts in the last couple of decades . I think that Steve and others by virtue of their careful analysis of the individual station data a strong case for a wholesale
re-examination of how global temperatures measures are arrived at. Dr. Wilson’s current paper provides a further rationale for such a re-examination.

Curiouser and curiouser: GHCN V2 has two sets of temperature data for
Dawson, Y.T. which include the early 20th century. They differ slightly.
They are each adjusted, but with very different adjustments. A few
samples below: the leading 0 or 1 is the set number, the first line of
each pair is “raw”, and the second line is adjusted. Take your pick.

Curiouser and curiouser: GHCN V2 has two sets of temperature data for
Dawson, Y.T. which include the early 20th century. They differ slightly.
They are each adjusted, but with very different adjustments. A few
samples below: the leading 0 or 1 is the set number, the first line of
each pair is “raw”, and the second line is adjusted.

I sent you an e-mail with the Environment Canada data for Dawson attached. I also cc’d John. Let me know if you did not get it and if you want it. You have my e-mail.

It looks like E.C. believes that only the annual average temperatures between 1977 and 2001 are valid.

Note to some others: Dawson is only at 64.2°N and therefore is not in the Arctic (>66°33’N). However it is probably included in the “Arcticish” locations used to suggest the Arctic is warming (as opposed to the actual Arctic stations which do not show the warming (or as much warming anyway)).

However, this does highlight an important issue. Tree-ring based reconstructions are “at the mercy” of the instrumental data and if there are problems with the predictand data, then it will affect our calibrations.

I would think that the whole theoretical approach would require rethinking rather than your calibrations.

These are the moments I’m glad that my research does not in any way depend on global or local temperature measurements. Maybe the only possibility of getting any ring/temp relationships is to have a thermometer attached to each tree studied😉

This whole thing is sufficiently important that that’s exactly what should be done. Monitor temperature, pressure, precipitation, windspeed, and local CO2 concentration at a couple thousand trees. Then systematically start varying conditions. Give one batch more CO2, or more water…

“This whole thing is sufficiently important that that’s exactly what should be done. Monitor temperature, pressure, precipitation, windspeed, and local CO2 concentration at a couple thousand trees. Then systematically start varying conditions. Give one batch more CO2, or more water…”

That would require expirements based on something other than a computer, and so would not be acceptable. Even the measurement of the effects of altitude, temperature and water vapor content on the absorbtion of IR by CO2 in the atmosphere appears to be best elucidated by computer modeling, rather than direct measurement.

#6 John Nicklin
You’re not being paranoid if they really are out to get you!

We really miss John Daly; he seemed to be prescient in his proactive archiving of data from various weather stations. With all of the dubious and seemingly arbitrary “adjustments” taking place, most of which seem to produce convenient results, why isn’t there some discussion of limiting the use of data to those from stations that can be shown to have remained rural. Even if these stations have been moved, as long as the rural character has essentially been maintained, wouldn’t a clearer record be provided?